Laser or optically based non-contact range sensor systems are used in dimensional metrology, such as the system disclosed in U.S. Pat. No. 6,288,786 B1, the disclosure of which is hereby incorporated by reference. These sensors generally have a limited range of operation and resolution within that range. The range of such a system is typically defined as the linear distance for which the sensor provides a useful distance measurement. The axial resolution of the sensor is usually defined as the smallest distance within the sensor's range that can be resolved by the sensor. Many of these sensors are used to measure distance along the vertical axis, usually the Z axis, but they can be set up to measure along any axis of choice.
There are several types of range sensor systems, and each sensor type has a range to resolution numerical ratio. This ratio can be a few hundred, or as high as a few thousand, depending on the design. Some companies claim an even higher ratio, but only by using a good deal of averaging while taking a measurement from a high quality very smooth mirror surface. An example of a device with which range sensors are used is a Coordinate Measuring Machine (CMM), such as that disclosed in U.S. Pat. No. 6,518,996, which is hereby incorporated by reference.
Several companies worldwide manufacture non-contact range sensors. One example of such a sensor is found in the DRS-500 (Digital Range Sensor 500) manufactured by assignee Quality Vision International, Inc., of Rochester, N.Y. Additional examples include the Conoprobe 1000 conoscopic holography-based non-contact, single-point measuring sensor by Optical Metrology, Ltd., (a.k.a. Optimet) of Jerusalem, Israel, the CHR-150 chromatic confocal sensor by STIL SA of Aix-en-Provence, France, and the LT-9000 laser confocal displacement meter by Keyence Corporation of Osaka, Japan. The different sensors of the prior art are configured to operate over a set range. Sensor ranges can be from tens of microns to a few millimeters, each range having an attendant resolution. Such prior art systems can provide long range capability with low resolution or short range capability with high resolution. However, there are times when long range capability would be very useful coupled with high resolution measurement. Current commercial arrangements do not provide a way to operate with both simultaneously.
To increase the range of use, yet still provide high resolution measurements, the system of embodiments disclosed herein has at least two different sensor systems that can be used sequentially or simultaneously, at least two of which operate in different resolutions and ranges. In a preferred embodiment, a very high resolution, but short range sensor, is combined with a lower resolution, but longer range sensor. Thus, embodiments provide a low resolution range sensor system that can operate in a first range of, for example (but not exclusively), about 0.5 mm, and a very high resolution range system that can operate in a second range of, for example (but not exclusively), 10 μm. The low resolution system can employ a position sensitive detector (PSD) in embodiments, or a linear CCD array detector in embodiments, in a triangulation optical system, which sensors allow for longer range detection and measurement. The high resolution system can use a dual photo diode detector (DPD) in another triangulation optical system. Other sensor types can be used in both the long range and short range sensor arrangements, though the PSD, CCD array, and DPD are here preferred.
The dual resolution optical system of embodiments can be configured in at least two ways. In a first configuration, a beam splitter splits the return beam and simultaneously sends the return beam components to both the long range sensor detector(s) and the short range sensor detector(s). In a second configuration, the system can alternate between the long range and short range sensor detectors, which allows more light to arrive at the respective sensor detectors.